<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 100%;
            height: 150px;
            background-color: red;
            display: flex;
            justify-content:flex-end;
        }

        div span {
            background-color: green;
            width: 100px;
        }
    </style>
</head>
<body>
      <div>
          <span>1</span>
          <span>2</span>
          <span>3</span>
      </div>
</body>
</html>